Every organism needs energy to live. But where does that energy come from? Let’s find out…

There are two types of organisms: autotrophs, which make their own food, and heterotrophs, which must consume food from an outside source.

Most autotrophs convert light energy from the sun into usable energy. These are the only types of autotrophs you need to be concerned with for now. Your typical autotroph would be any plant, a grass, a tree, a shrub. Unicellular organisms can be autotrophs too!

Examples of heterotrophs include animals, such as yourself or a lion, as well as fungi plus some unicellular organisms like some protists or bacteria.

Energy comes in many forms. We already mentioned light energy from the sun. There’s also heat energy and other types like the electricity that powers your television.

The type of energy that cells can best use is chemical energy. Specifically it’s in the form of a chemical called ATP. Really the only thing you need to know is that ATP is like a fully charged battery. A bond is broken and energy is released. That turns ATP into ADP. Or you can think of it like this A3P =>release of energy => A2P. ADP is like a battery waiting to be recharged.

ADP + Engery stored = ATP

For some reason this seems to really trip people up. If you have any questions, drop me a comment or a tweet @AmoebaMike.

Animal cells and plant cells. Fungal cells and bacteria cells. Turns out cell are even more diverse than that. A unicellular organism, like a typical bacterium, grows and operates alone. It may hang out with other cells, but they are all on their own. Some organisms however, are multicellular, and in more complex organisms these cells specialize what they do.